The objectives of this research project are: 1) investigation of the effects of DES and sex steroids (estrogens, progesterone, testosterone) on the course of rat pregnancy and on the transplacentally and transmammary exposed offspring; 2) elucidation of the mechanisms by which DES and sex steroids influence development and differentiation of the urogenital apparatus of the rat fetus and the neonatal rats; 3) investigation of the relationship of DES- and sex steroid-induced disturbance in transformation of vaginal Mullerian (columnar) epithelium into squamous epithelium and subsequent development of genital cancer; 4) determination of the usefulness of the pregnant rat as a screeening model for estrogenic or other substances potentially teratogenic and carcinogenic to the human fetus and offspring.